Sergeant said researchers at MessageLabs see about 2 million different computers in the botnet sending out spam on any given day, and he adds that he estimates the botnet generally is operating at about 10 percent of capacity. 'We've seen spikes where the owner is experimenting with something and those spikes are usually five to 10 times what we normally see,' he said, noting he suspects the botnet could be as large as 50 million computers. 'That means they can turn on the taps whenever they want to.'